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The Bose-Einstein Condensation of dilute atomic gases is the subject of intense studies since its first demonstration in 1995. Our group is expert in manipulating atoms in radiofrequency dressed potentials. Our current experimental studies in this field focus on testing the superfluidity of degenerate Bose gases in a toroidal trap. We are also interested in the physics of ultracold gases in lower dimensions (1D, 2D).
Fig. 1: a Rb BEC produced in a plugged
quadrupole trap, imaged after
a 25 ms time of flight (TOF).
Fig. 2: TOF image of a BEC in a dressed quadrupole trap.
Rubidium BEC produced in a plugged quadrupole trap
We produce a pure Rb BEC with 2.105 atoms after 20 s of RF evaporation in a quadrupole trap plugged with a 532 nm laser beam focused on 40 micrometers (Fig. 1). At first, the evaporation takes place in the linear (quadrupole) trap. Below 100 µK, the laser beam is essential against Majorana losses, largest at lower temperature in a pure quadrupole trap. At very low temperatures, the plugged trap is harmonic, and its oscillation frequencies are measured by resonant excitation.
Quantum gases in low dimensions
We have demonstrated the confinement of ultra cold atoms in a very anisotropic - pancake - trap. The atoms first condensed in a quadrupole plugged by a blue detuned laser to prevent Majorana losses. They are then dressed with a radio-frequency (RF) field to be confined to an iso-magnetic surface of the quadrupole. As the laser is slowly switched off, the BEC follows the trapping surface to its bottom. The vertical oscillation frequency, due to the RF field, is then much larger than the horizontal ones, only due to gravity (pendulum frequencies), which is visible on Fig. 2 where the cloud after time of flight has become very anisotropic.
Superfluid rotating in a ring geometry
The combination of the dressed bubble-shaped trap with a vertical standing light wave gives rise to a ring trap, as we recently proposed. We also proposed theoretically a technique to rotate the trapped atoms, which opens the way to experiments on superfluidity in a circular geometry. Adding the standing wave will be the next step in our experiment.
In a recent theoric work, we studied the effect of a quantum anomaly on a Bose gas confined to 2 dimensions. The anomaly produces a small shift of the frequency of the breathing mode. We proposed a way to observe this effect in an experiment.
The BEC group is a membre of IFRAF.
Vincent Lorent, Hélène Perrin